The Vaisala National Lightning Detection Network (NLDN) has been in operation since 1989. The Vaisala Long Range Lightning Detection Network (LLDN) is a much newer capability utilizing NLDN sensors and Canadian Lightning Detection Network (CLDN) sensors to detect cloud-to-ground lightning flashes up to two thousand kilometers off the coasts of North America. In addition, Vaisala's LLDN includes several long range sensors located in the North Pacific Ocean.

LLDN detection efficiency decreases with increasing distance from NLDN, CLDN and North Pacific Ocean sensors. In addition, detection efficiency varies as a function of time of day due to lightning signal propagation interaction with the ionosphere. LLDN detection efficiency is higher during the night than during the day due to better ionospheric propagation conditions at night. Detection efficiency that varies as a function of location and time of day introduces challenges for monitoring lightning rates within tropical cyclones that are in motion.

Vaisala has recently studied inner core lightning rates in many tropical cyclones that have occurred since 2003. A lightning flash was considered to have occurred in the inner core of a tropical cyclone if it was located within 100 km of the center of the tropical cyclone, as reported by the National Hurricane Center (NHC), and within 90 minutes of the NHC reported location. These first analyses did not take into account the varying detection efficiency within the LLDN mentioned above. This paper will discuss inner core lightning rates produced by 2005-2006 Atlantic and East Pacific tropical cyclones after night-time detection efficiency corrections have been applied to the LLDN data that also take into account location. Since the LLDN has a higher detection efficiency at night than during the day, these corrections represent conservative estimates of inner core lightning rates within tropical cyclones. Results from this analysis show that lightning production within the inner core of tropical cyclones is higher than one might expect from previous studies using NLDN data or aircraft reconnaissance reports. Inner core lightning rates as a function of tropical cyclone intensity will also be discussed.